Pyrotechnic drop mechanism for power tools

ABSTRACT

A saw includes a surface defining an opening therein, a plate structure configured to be attached to the saw below the surface, and an arm attached to the plate structure about a first shaft. A blade is configured to be engaged with the arm at a location spaced from the first shaft. The blade extends through the opening when the saw is in a normal operating position. The saw includes a firing mechanism including a barrel end portion having a bore defined therein and an extendable piston at least partially positioned within the bore. The barrel end portion is attached to the plate structure. The extendable piston engages the arm during its extension and causes the arm to pivot about the first shaft when the firing mechanism is activated by an activation signal. The pivoting of the arm causes the blade to be moved downwardly below the surface.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of, and hereby claims priority under35 U.S.C. §120 to, U.S. patent application Ser. No. 11/589,344, filedOct. 30, 2006 now U.S. Pat. No. 7,628,101, by William R. Knapp et al.,entitled PYROTECHNIC DROP MECHANISM FOR POWER TOOLS, which is acontinuation of, and claims priority under 35 U.S.C. §120 to, U.S.patent application Ser. No. 11/374,319, filed Mar. 13, 2006 nowabandoned, by William R. Knapp et al., entitled PYROTECHNIC DROPMECHANISM FOR POWER TOOLS, which claims priority under 35 U.S.C. §119(e)to, U.S. Provisional Patent Application Ser. No. 60/660,788, filed Mar.11, 2005, by William R. Knapp et al., entitled PYROTECHNIC DROPMECHANISM FOR POWER TOOLS.

BACKGROUND OF THE INVENTION

The present invention generally relates to power tools and to bladedropping systems for such power tools.

Systems have been developed and are described in a plurality of patentapplications that are assigned to SD2, LLC which include variousmechanisms that have a detection system for detecting contact between ahuman and a blade The detection system triggers a brake mechanism thattypically includes a pawl structure that is urged into the blade by abiasing mechanism that is retained by a fusible member and is melted bya high energy electrical current. Severing the fusible member releasesthe pawl to stop the blade or to retract it below the work surface of atable saw, for example. The systems have disadvantages; for example theyare expensive and inconvenient to use since they require the replacementof expensive modules after they have been fired, which is time-consumingand difficult. An additional disadvantage is the variability of thesystem based on the blade design.

SUMMARY OF THE INVENTION

Embodiments of a saw are disclosed of the type which has a top with anopening in the top through which a saw blade can extend, the height andangular orientation of which can be adjusted, and also configured to beretracted in response to an activation signal being applied, the sawcomprising a plate structure configured to be mounted to the saw belowthe top, an arm pivotally mounted to the plate structure about a firstshaft, a rotatable circular blade having an arbor mounted to the arm ata location spaced from the first shaft, and being configured so that atleast a portion of the blade can extend through the top opening and bein position to cut a work piece when the blade is in its normaloperating position, a drive motor with an output shaft operativelyconnected to power the saw blade, a firing mechanism having a barrel endportion with a cylindrical bore mounted to the plate structure and anextendable piston positioned in the bore, the piston engaging the armduring its extension and causing the arm to pivot about the first shaftwhen the firing mechanism is activated by the activation signal beingapplied, the pivoting of the arm causing the blade to be moveddownwardly below the saw top toward its retracted position.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a preferred embodiment of the blade retractingmechanism, showing the blade in the normal operating position;

FIG. 2 is a cross section of a portion of the apparatus shown in FIG. 1,particularly illustrating the pyrotechnic firing mechanism;

FIG. 3 is a side view of the apparatus shown in FIG. 1, but illustratingthe saw blade in a partially retracted position;

FIG. 4 is a view similar to FIG. 2, but showing the firing mechanismimmediately after firing when the piston is at the extent of its travel;

FIG. 5 is a side view of the apparatus shown in FIG. 1, but illustratingthe saw blade in a fully retracted position;

FIG. 6 is a view similar to FIG. 2, but showing the firing mechanismafter firing but with the piston reacting back to its post firingresetting position;

FIG. 7 is a side view of a portion of a second embodiment of the bladeretracting mechanism and is shown with the blade in a normal operatingposition;

FIG. 8 is a view of the apparatus shown in FIG. 7, but illustrating theblade in a fully retracted position;

FIG. 9 is an idealized perspective view of a portion of the apparatusshown in FIG. 8, with the blade in its normal operating position; and

FIG. 10 is a similar perspective view of a portion of the apparatusshown in FIG. 9 illustrating portions of the mechanism that were hiddenfrom view in FIG. 9.

DETAILED DESCRIPTION

The preferred embodiments of the blade retracting mechanism that areshown and described herein are operable with a detection system that isdesigned and configured to be able to detect the presence of a personeither by use of a mechanism that detects the proximity of a person'shand or possibly by virtue of detection of contact of a person's bodywith a portion of the saw or other tool that is designed to be a sensor.The most likely component to be used as a sensor is the saw blade, whichwould be used to detect the person's proximity or contact with a sawblade. If contact with a saw blade is necessary for detection, therewould necessarily be at least some injury to a user depending upon thespeed of approach and the speed in which the entire system operates.

The preferred embodiment of the present invention is shown in FIGS. 1-6,with FIG. 1 showing a side view of a blade retracting mechanismindicated generally at 10, with the blade 12 being in a normal operatingposition, where the blade is near a riving knife 14. In FIG. 3, theblade 12 is shown to be partially retracted as would occur duringoperation of the mechanism 10 and in FIG. 5, the blade 12 is fullyretracted below the surface of the table saw top which is approximatelyat the elevation shown by the dotted line T of FIGS. 1, 3 and 5. Theblade 12 rotates on a shaft 16 that is journaled in a generallytriangularly shaped arm 18 that has a curved lower surface 20. The arm18 rotates around another shaft 22 that is attached to a large plate 24that is mounted to the saw by mounting brackets 26 and 28 located onopposite ends of the plate 24. The plate 24 carries a motor base 30 thatis mounted above the elevation of the plate 24 and carries a motor 32for driving the saw blade 12.

The output shaft of the motor 32 is not shown, but it carries a pulleywhich drives a belt 34 and a pulley 36, with the pulley 36 beingconnected to another pulley or having an extension for driving a belt 38and in turn drives a pulley 40 that is operatively connected by theshaft 16 to an arbor (not shown), but which drives the blade 12. Sincethe arm 18 is pivotable about the shaft 22, it should be understood thatthe motor 32 is configured to be able to drive the belts 34 and 38 viathe motor pulley and pulley 36 regardless of the vertical position ofthe blade 12. Stated in other words, the distance between pulleys 36 and40 remains constant as does the distance between pulley 36 and the motordrive shaft regardless of the vertical position of the blade 12.

When the blade is in the normal operating position as shown in FIG. 1,the top right surface of the arm 18 abuts against a stop member 41 thatis mounted to the plate 24 by a mounting bracket 42 with bolts 44. Thearm 18 is held in the upper position as shown in FIG. 1 by a detentassembly, indicated generally at 46, that comprises a main bracket 48that is bolted to the plate 24 by bolts 50 and wherein a detent rod 52engages a V-shaped recess 54. The rod 52 is biased into engagement withthe recess 54 by a spring 56 that is seated on a bolt 58 and which isadjustable to vary the biasing force that is applied to the rod 52. Thedetent assembly 46 is therefore designed and configured to maintain thearm 18 in its normal operating position unless it is rotated downwardlywith sufficient force to depress the detent rod 52 away from theV-shaped recess 54 and release the arm 18 for rotation.

The force that is necessary to overcome the detent assembly 46 isprovided by a firing mechanism that is indicated generally at 60. Across-section of the mechanism is shown in FIGS. 2, 4 and 6, andcomprises a cylindrical barrel structure 62 having a cylindrical bore 64in which a piston 66 is positioned. The mechanism 60 has a replaceablecartridge 68 that is placed in a smaller bore 70 with the cartridge 68being retained by an end cap structure 72 through which a metal pin 74is located with the pin extending to the cartridge 68 so that it can befired. The pin 74 is connected to a wire 76 which in turn is connectedto a capacitor 78.

During operation, the capacitor 78 is switched to release its electricalcharge which travels through wire 76 to heat the pin 74 to a temperaturethat fires the cartridge 68 and this causes high pressure gases to beproduced and cause the piston 66 to be moved to the left out of the bore64. The piston 66 is guided by a support 80 having a cylindrical openingtherein sized to receive the cylindrical piston 66. As it is driven inthe leftward direction, i.e., away from the barrel 62, a hammer 82 isdriven toward a hammer damper 84 that is mounted to a skid 86 that alsohas a mounting structure, indicated generally at 88, which holds thedamper 84 and cushions the hammer 82. During its travel the hammer 82drives the arm 18 in the clockwise direction around the shaft 22. Thepiston 66 has an enlarged end portion 90 that defines a shoulder 92 thatengages the support member 80 at the end of its travel. It should alsobe understood that the skid 86 and support member 80 are effectivelyconnected together. An end bracket 94 has a narrow center portion 96that extends rearwardly and it is retained by a pair of support members98 (FIG. 1) located on opposite sides of the center portion 96. Thesupport members 98 are bolted to the plate 24 by bolts 100.

An anvil 102 is connected to the arm 18 by a pair of pins 104 and a pairof bolts 106 as well as by a strap 108 that is bolted on opposite endsto the anvil 102 and the arm 18. It should be apparent that the frontsurface of the hammer 82 is in contact with the adjoining surface of theanvil 102 so that when the firing mechanism 60 is activated, the piston66 will cause the hammer 82 to move the anvil 102 and arm 18 in aclockwise direction so as to retract the blade 12 below the surface Tbefore the user is seriously injured.

When the microprocessor triggers the pyrotechnic device, a high amperagecurrent is sent through the wire 76 to the electrode or pin 74, whichdirects the current to the back of the cartridge 68. The cartridge 68fires causing a rapid pressure rise in the barrel 62 behind the piston66 that produces approximately 10,000 pounds of force that propels ittoward the anvil 102. The piston 66 is forced to move along the barrelaxis pushing the anvil 102 as it does so. This pushing force overridesthe detent assembly 46 and the arm 18 rotates in a clockwise direction.When the arm 18 moves to its position of maximum travel as shown in FIG.5, the hammer 82 fully compresses the hammer damper 84. In thisposition, the barrel 62 vents the combustion gases because the piston 66moves past the end of the barrel 62 thus relieving the barrel pressurein preparation to stopping the piston 66. Since the arm 18 and hammer 82are not physically connecting, i.e., they only touch, the arm 18 is freeto continue rotating even though the piston 66 stops. The arm 18continues to rotate until it contacts a mechanical stop that is notshown, at which time its movement ends. The hammer damper 84 thenrelaxes and pushes the hammer 82 and piston 66 back into the barrel 62.The cartridge 68 is a commonly available 22 caliber nail gun cartridgethat is used in construction and costs about $0.05. An advantage of thepreferred embodiments of the present invention is that once thecartridge 68 is fired, the end cap 72 can be removed enabling the spentcartridge shell to be removed. The firing mechanism 60 can be rearmed byplacing another cartridge 68 in the bore 70, inserting another pin 74 inthe end cap 72, connecting the wire 76 to the pin and recharging thecapacitor 78.

In a second preferred embodiment shown in FIGS. 7-10, reference numbersthat have been given to the first preferred embodiment shown in FIGS.1-6 are used where the components are similar. In the embodiment shownin FIG. 7, the arm 18 has structure that interacts with a detentassembly 46 in a slightly different manner, i.e., the V-shape recess 54is not directly contacted by the detent rod 52, but contains anextension piece 112 that extends beyond the curved surface 20 of the arm18 and contacts the end of the detent rod 52 as shown.

This extension is necessary because of a slight modification to theplacement of the detent assembly 46 to accommodate the addition of ananti-bounce mechanism, indicated generally at 114 that is located belowthe anvil 102. The outer surface 20 of the arm 18 has a number ofserrated teeth 116 along a portion of the surface which are positionedto engage a ratchet assembly 118 that pivots about a shaft 120 that isoperatively connected to the plate 24. A compression spring 122 has oneend engaging an extension 124 of the ratchet assembly and the oppositeend bearing against a bracket 126 so that a pawl 128 of the ratchetassembly 118 is biased toward the arm 18.

As shown in FIG. 8, the saw blade 12 is mounted to the arm 18 through anaperture in the plate 24 by the shaft 16. The aperture in the platecomprises an arcuately-shaped track 21 such that when the arm 18 rotatesclockwise about the shaft 22, the shaft 16 moves downwardly along thearcuately-shaped track 21. After the firing mechanism 60 rotates the arm18 in a clockwise direction, its left surface 130 will contact a stop ordamper 132. Because of the tremendous force having been applied to thearm 18, the arm 18 is moving rapidly and bounces off the stop 132. Asshow in FIG. 8, as the arm 18 bounces off of the stop 132, the pawl 128will engage one of the teeth 116 and stop the counterclockwise movementof the arm 18 and prevent the blade 12 from moving upwardly above thetabletop to potentially strike the user. While not shown, a pull leveris preferably provided to release the pawl 128 from the teeth 116 as thearm 18 is returned to its normal operation position. While adjustable,it is preferred that the amount of force needed to release the pawl 128be in the range of about 10 to about 20 pounds. The amount of forceneeded to lift the arm 18 to its normal operation position is within therange of about 10 to about 20 pounds and the amount of force to overcomethe spring 56 in the detent assembly 46 to latch the arm 18 in thenormal operating position is preferably within the range of about 15 toabout 25 pounds.

While various embodiments of the present invention have been shown anddescribed, it should be understood that other modifications,substitutions and alternatives are apparent to one of ordinary skill inthe art. Such modifications, substitutions and alternatives can be madewithout departing from the spirit and scope of the invention, whichshould be determined from the appended claims.

1. A table saw configured to retract a saw blade in response to anactivation signal from a normal operating position, where the saw bladeextends out of an opening in a table top of the table saw, into aretracted position, where the upper reach of the saw blade is positionedbelow the table top, the table saw comprising: a plate mounted to thetable saw below the table top, wherein an arcuately-shaped track isdefined in the plate; an arm pivotally mounted to the plate about afirst shaft; a second shaft mounted to the arm at a location spaced adistance from the first shaft and extending into at least a portion ofthe arcuately-shaped track, wherein the second shaft comprises an arbor,and wherein the arbor is engagable with the saw blade; a detent assemblymounted to the plate and configured to releasably engage the arm to holdthe arm in position when the saw blade is in the normal operatingposition; and a firing mechanism comprising: a barrel comprising a bore;and an extendable piston positioned at least partially within the bore,wherein the piston is configured to cause the arm to pivot about thefirst shaft when the firing mechanism is activated by the activationsignal, wherein the pivoting of the arm overrides the detent assemblyand causes the second shaft to move downwardly along thearcuately-shaped track, and wherein the downwardly movement of thesecond shaft along the arcuately-shaped track brings the saw blade belowthe table top into the retracted position.
 2. The table saw as definedin claim 1 wherein the arm comprises an anvil portion mounted to aportion thereof, wherein the piston comprises a hammer mounted on aportion thereof, and wherein the hammer is configured to engage theanvil portion to pivot the arm about the first shaft through an arcsufficient to lower the saw blade below the table top into the retractedposition.
 3. The table saw as defined in claim 1 wherein the barrelcomprises a removable end cap portion, wherein the barrel is mounted tothe plate, wherein removal of the end cap portion reveals a small borethat is in communication with a larger bore in the barrel, wherein thesmall bore is configured to receive a pyrotechnic cartridge, and whereinthe end cap portion is configured to accept a pin that is connectable toa power source for heating the pin to cause the cartridge to fire. 4.The table saw as defined in claim 1 wherein the piston comprises ahammer configured to engage and push the arm when the firing mechanismis activated by the activation signal, and wherein the pushing causesthe arm to pivot about the first shaft and override the detent, therebybringing the saw blade below the table top into the retracted position.5. The table saw as defined in claim 1 wherein the arm comprises anarcuately-shaped outer surface, and wherein the arcuately-shaped outersurface of the arm comprises at least two teeth.
 6. The table saw asdefined in claim 5 comprising a ratchet assembly comprising a ratchetmember that is biased toward the at least two teeth and configured toengage at least one of the at least two teeth to counter kick-back ofthe arm after activation of the firing mechanism.
 7. The table saw asdefined in claim 1 wherein the arm is configured to travel at leastpartially along the arcuately-shaped track when the saw blade is movedfrom the normal operating position into the retracted position.
 8. Thetable saw as defined in claim 1 wherein the arm comprises a curved outersurface, wherein the curved outer surface comprises a plurality ofteeth, wherein the table saw comprises a ratchet assembly comprising aratchet member that is biased toward the plurality of teeth andconfigured to engage at least one of the plurality of teeth to counterkick-back of the arm after activation of the firing mechanism.
 9. Thetable saw as defined in claim 1, wherein arm comprises a generallypie-shaped arm pivotally attached to the plate about a first shaft. 10.The table saw as defined in claim 9 wherein the arm comprises a curvedouter surface, and wherein the curved outer surface defines an arcwithin the range of about 70 to about 90 degrees.
 11. The table saw asdefined in claim 9 wherein the arm is configured to travel at leastpartially along the arcuately-shaped track when the saw blade is movedbelow the working surface into the retracted position.
 12. The table sawas defined in claim 9 wherein the firing mechanism comprises a barrelcomprising a removable end cap portion, wherein the barrel defines abore and is mounted to the plate, and wherein the piston is at leastpartially positionable within the bore when in the first unfiredposition.
 13. The table saw as defined in claim 9 wherein the table sawcomprises a detent assembly mounted to the plate and configured toreleasably engage the arm to releasably hold the arm in position whenthe saw blade is in the normal operating position.
 14. The table saw asdefined in claim 9 wherein a face of the plate defines a generallyhorizontal plane, and wherein a direction of motion of the arm, whenpivoting, is substantially parallel to the generally horizontal plane.15. The table saw as defined in claim 9, wherein the arm comprises atleast two teeth, and further comprising a ratchet assembly comprising aratchet member biased toward the at least two teeth and configured toengage at least one of the at least two teeth to counter kick-back ofthe arm.
 16. The table saw as defined in claim 1 wherein the piston isconfigured to be moved between a first unfired position, where the sawblade is in the normal operating position, and a second fired position,where the saw blade is moved into the retracted position below the tabletop, and wherein the piston is free from engagement with the arm in thefirst unfired position.
 17. The table saw as defined in claim 16 whereinthe piston comprises a hammer configured to engage and push the arm whenthe piston moves from the first unfired position to the second firingposition, and wherein the pushing causes the arm to pivot about thefirst shaft and override the detent assembly.
 18. The table saw asdefined in claim 1 wherein the plate is disposed between the arm and thesaw blade and wherein the arm engages the saw blade across the platethrough an aperture in the plate.
 19. The table saw as defined in claim18 wherein the aperture comprises the arcuately-shaped track.
 20. Thetable saw as defined in claim 19 wherein when the saw blade is broughtbelow the table top into the retracted position, the saw blade movesdownwardly along the arcuately-shaped track and adjacent to the pointwhere the second shaft is mounted to the arm.
 21. The table saw asdefined in claim 1 wherein extension of the piston causes the arm topivot about the first shaft when the firing mechanism is activated bythe activation signal.